Ab initio calculations and three different applications of unimolecular rate theory for the dissociations of CCl{sub 4}, CFCl{sub 3}, CF{sub 2}Cl{sub 2}, and CF{sub 3}Cl

Journal Article · Thu May 02 00:00:00 EDT 1996 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/jp9600470· OSTI ID:249665

Kumaran, S S; Su, M C; Lim, K P; Michael, J V; Wagner, A F; Harding, L B ^[1]; Dixon, D A ^[2]

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1. Argonne National Lab., IL (United States)
2. DuPont Central Research and Development Experimental Station, Wilmington, DE (United States)

Previously measured Cl dissociation rate constants for CCl{sub 4} and CFCl{sub 3} were analyzed with three different kinetics modeling calculations. The three models differ in detail but primarily are distinguished by the manner in which the high-pressure limiting rate constant is determined: model 1 involves a calibration to transport properties of the dissociated fragments, model 2 uses a Gorin model with a hindrance parameter, and model 3 requires variational transition state thoery on an ab initio reaction path where all low-frequency motion off the path is presumed to be a free rotation. All three models have two adjustable parameters: the dissociation energy E{sub 0} and the average energy transferred to the buffer gas [{Delta}]{sub down}. All three models are found to give comparable fits to the experiment and produce quite similar values for the adjustable parameters. The values for CCl{sub 4} and CFCl{sub 3} are compared to those obtained in similar studies for CF{sub 2}Cl{sub 2} and CF{sub 3}Cl. The results indicate a substantial and consistent decrease in the C-Cl bond energy with each additional chlorine substitution in the chlorofluoromethanes. Isodesmic electronic structure calculations at the MP2 level confirm this effect but find it to be a little smaller than the experimental results indicate. Extended electronic structure calculations provide heats of formation for all nine CF{sub x}F{sub y}Cl{sub z} methyl radicals. 42 refs., 4 figs., 5 tabs.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 249665
• Journal Information: Journal of Physical Chemistry, Vol. 100, Issue 18; Other Information: PBD: 2 May 1996
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
66 PHYSICS
99 MATHEMATICS
COMPUTERS
INFORMATION SCIENCE
MANAGEMENT
LAW
MISCELLANEOUS
CARBON TETRACHLORIDE
CHEMICAL REACTION KINETICS
DISSOCIATION
ORGANIC FLUORINE COMPOUNDS
ORGANIC CHLORINE COMPOUNDS
HYDROCARBONS
METHYL RADICALS
FORMATION HEAT
THEORETICAL DATA
MOLECULAR MODELS
CALCULATION METHODS
ELECTRONIC STRUCTURE